It is known to prepare oxalic esters by oxidative reaction of carbon monoxide and monobasic alcohols with oxygen and also with quinones, preferably in a substantially anhydrous medium, anhydrous for the presence of dehydrating substances, and catalyzed by Redox-systems in general consisting of the finely subdivided metal or of soluble salts or complexes (citrates, chelates) of a noble metal of the Pt group, such as, for instance, Pd, Os, and of a salt and/or a complex of another metal more electropositive than the previous ones, such as Fe, Co, Ni, Cu, Mn, etc., such as chlorides, acetates, etc., possessing several oxidative states.
The reaction is preferably conducted in the presence of co-catalysts and/or complexing agents consisting of soluble salts of alkaline metals (e.g., LiCl, KCl, etc.).
Nevertheless, processes of this type, because of the simultaneous occurrence of secondary reactions leading to the formation of carbonates, CO.sub.2, esters-(acetates, formates, etc.), cannot be considered fully satisfactory from the industrial point of view owing to the low yields and because of the relatively burdensome operations involved, such as separation, purification, etc.
Moreover, the use of gaseous CO+O.sub.2 mixtures with the corresponding risk of explosions constitutes a further serious obstacle to an industrial application.
On the other hand, the other processes of the prior art, for instance, by the dehydrogenation of sodium formate, subsequently converted to calcium oxalate, acidified, etc., or by oxidation of the propylene with HNO.sub.3 catalyzed by Fe, Cr, etc., do not insure best results owing to the considerable technological and operational difficulties involved which make them little acceptable economically, especially for the mass production.